534 PHYSIOLOGY OF GROWTH. 



autonomous movements are in the same direction or opposed 

 to the paratonic and daily periodic movements will the moments 

 of these latter be amplified or lessened. (For further particulars 

 see Pfeffer.) 



1 See Pfeffer, Die periodischen Bewegungen der Blattorgane, 1875, pp. 9 and 

 97. 



201. Experiments with Mimosa pudica and other Plants. 



The leaflets of Mimosa pudica perform movements both as the 

 result of shock or contact and in consequence of changes in 

 illumination, and these are effected by the pulvini of the primary 

 and secondary leaf-stalks and of the individual leaflets. The 

 plants may be raised from seed in flower-pots ; care must be taken 

 in cultivating them that they are exposed to a high temperature 

 (20-25 C.), and that they are well supplied with water. This 

 last is best attained, in cultures carried on in an ordinary room, 

 by covering the plants with large bell-glasses soon after they 

 appear above ground, without of course interfering too much 

 with the circulation of the air. A good number of seedlings may 

 be grown in the same pot, but they are early transplanted into 

 separate ones, and the cultivation is continued in warm moist air 

 at the window. In vigorous plants the main leaf-stalk is daring 

 the day more or less upwardly directed, and the leaflets are 

 expanded. If in the daytime we suddenly darken a plant, by 

 placing over the covering bell-glass a cardboard box, the main 

 leaf-stalk raises itself not inconsiderably, so that the angle which 

 it makes with the stem becomes more acute, and the leaflets lay 

 themselves together in an upward direction. If the Mimosa 

 plants under the bell-glasses are left in the daytime, untouched, 

 to the influence of the light, it is seen that the leaflets lay them- 

 selves together towards evening, and that the main leaf -stalks 

 sink as darkness comes on. Thus in Mimosa pudica sudden 

 darkening during the day on the one hand, and the normal even- 

 ing darkening on the other, act in the same manner on the leaflets, 

 but do not act in the same manner on the main leaf-stalks. 1 



If plants of Mimosa, at first cultivated under normal conditions, 

 are exposed in a sufficiently moist atmosphere to constant dark- 

 ness, they exhibit after some time, like Acacia and Phaseolus, 

 after-effect movements of the leaves, i.e. the leaflets are spread out 

 in the daytime, and laid together at night-time. Gradually these 



